> On Sep 18, 2016, at 7:25 AM, mviljamaa <mvilja...@kapsi.fi> wrote: > > What are the red line and cut line in lm's Residuals vs Fitted plot? > > As seen in e.g.: > > http://i.imgur.com/QvZ6oeT.png

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R has a `plot.lm` function that is invoked by `plot(lm_object)` when `lm_object` has a class of "lm". It produces multiple diagnostic plots. The default is for display of 4 of the possible 6 plots. The help page can be specifically accessed by: ?plot.lm And run the first example: lm.SR <- lm(sr ~ pop15 + pop75 + dpi + ddpi, data = LifeCycleSavings) plot(lm.SR) If you have further question about that particular plot, which would be the first one, you should first review the help page and then review the code seen with: plot.lm #Error: object 'plot.lm' not found getAnywhere(plot.lm) # the way to see code that is not exported: See: function (x, which = c(1L:3L, 5L), caption = list("Residuals vs Fitted", "Normal Q-Q", "Scale-Location", "Cook's distance", "Residuals vs Leverage", expression("Cook's dist vs Leverage " * h[ii]/(1 - h[ii]))), panel = if (add.smooth) panel.smooth else points, sub.caption = NULL, main = "", ask = prod(par("mfcol")) < length(which) && dev.interactive(), ..., id.n = 3, labels.id = names(residuals(x)), cex.id = 0.75, qqline = TRUE, cook.levels = c(0.5, 1), add.smooth = getOption("add.smooth"), label.pos = c(4, 2), cex.caption = 1, cex.oma.main = 1.25) Note: I checked the option setting with: > getOption("add.smooth") [1] TRUE ---snipped plotting set up logic ----- if (show[1L]) { ylim <- range(r, na.rm = TRUE) if (id.n > 0) ylim <- extendrange(r = ylim, f = 0.08) dev.hold() plot(yh, r, xlab = l.fit, ylab = "Residuals", main = main, ylim = ylim, type = "n", ...) panel(yh, r, ...) # this is what is drawing the "red line" if (one.fig) title(sub = sub.caption, ...) mtext(getCaption(1), 3, 0.25, cex = cex.caption) if (id.n > 0) { y.id <- r[show.r] y.id[y.id < 0] <- y.id[y.id < 0] - strheight(" ")/3 text.id(yh[show.r], y.id, show.r) } abline(h = 0, lty = 3, col = "gray") # this is drawing the dotted line dev.flush() So the `panel` function is creating the "red line" and its help page is at: ?panel.smooth #... ... since the `panel funciton was given that value. -- David. > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. David Winsemius Alameda, CA, USA ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.